This study aims to examine the epidemiology of the several specific components of late fetal death and neonatal mortality in a very large data set: all births in New York City (NYC) from 1957-1983. One series of analyses will identify the specific components of the declining time trends in perinatal mortality in NYC between the late 1950's and the early 1980's and explore the reasons for it. Within narrow birthweight categories, mortality trends will be examined to see whether they can be explained by changes in the distributions of maternal age, parity, or socioeconomic status of the birth population. Birthweight-specific analyses will be carried out separately for antepartum, intrapartum, and neonatal mortality trends. A specific objective will be to understand the relationship between obstetric intervention in labor and delivery and secular trends in perinatal mortality, especially fetal death during labor. Correlations between mortality and rates of cesarean section, induction of labor, and mid-and high-forceps delivery will be examined in time series regression analyses. Other analyses will examine maternal age and parity in relation to each component of mortality. Over a fourteen year period (1970-1983), fetal deaths during labor will be analyzed with age and parity as continuous variables. Prior fetal loss and socioeconomic indicators will be closely controlled. The role of birthweight, gestational age, and pregnancy complications (e.g. preeclampsia, abnormal uterine bleeding, diabetes) as intervening variables will be explored with path analytic techniques. Special attention will be paid to the risk among women in their thirties having their first birth, and the effect of cesarean section on risk. Birth cohort analyses will be carried out to test the possibility that a woman's birth cohort, rather than her age at delivery, determines mortality risk in her offspring.